System and method for replacing degenerated spinal disks

ABSTRACT

A system and method for replacing degenerated spinal disks in accordance with the present invention can substitute for interbody fusion techniques by replacing degenerated spinal disks with artificial spinal disks. In one embodiment, the system can comprise one or more artificial spinal disks, each comprising an upper and lower housing, a first spacer and a second spacer partially enclosed by a cavity formed by the housings, and a shaft with a spring positioned between the first spacer and the second spacer such that the spacers are urged apart.

CROSS-REFERENCED CASES

The following U.S. Patent Applications are cross-referenced andincorporated herein by reference: ARTIFICIAL VERTEBRAL DISK REPLACEMENTIMPLANT WITH TRANSLATING PIVOT POINT AND METHOD, U.S. Provisional PatentApplication No. 60/422,039, Inventor: James F. Zucherman et al., filedon Oct. 29, 2002; ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITHTRANSLATING PIVOT POINT AND METHOD, U.S. patent application Ser. No.10/684,669, Inventor: James F. Zucherman et al., filed on Oct. 14, 2003;ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH CROSSBAR SPACER ANDMETHOD, U.S. Provisional Patent Application No. 60/422,021, Inventor:Steve Mitchell, filed on Oct. 29, 2002; ARTIFICIAL VERTEBRAL DISKREPLACEMENT IMPLANT WITH CROSSBAR SPACER AND METHOD, U.S. patentapplication Ser. No. 10/684,668, Inventor: Steve Mitchell, filed on Oct.14, 2003; ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH A SPACERAND METHOD, U.S. Provisional Patent Application No. 60/422,022,Inventor: Steve Mitchell, filed on Oct. 29, 2002; ARTIFICIAL U.S. patentapplication Ser. No. 10/685,011, Inventor: Steve Mitchell, filed on Oct.14, 2003.

TECHNICAL FIELD

The present invention relates to spinal disks and spinal diskreplacement devices.

BACKGROUND

A common procedure for handling pain associated with degenerative spinaldisk disease is the use of devices for fusing together two or moreadjacent vertebral bodies. The procedure is known by a number of terms,one of which is vertebral interbody fusion. Interbody fusion can beaccomplished through the use of a number of devices and methods known inthe art. These include screw arrangements, solid bone implantmethodologies, and fusion devices which include a cage or othermechanism which is packed with bone and/or bone growth inducingsubstances. All of the above are implanted between adjacent vertebralbodies in order to fuse the vertebral bodies together, alleviatingassociated pain.

There are a number of drawbacks to undergoing interbody fusion. Onedrawback is that interbody fusion at one or more levels of the spine maycause decreased motion of the spine. Another drawback is that havinginterbody fusion at one or more levels of the spine may cause morestress to be transferred to adjacent levels. Transferred stress maycause new problems to develop at other levels of the spine, which maylead to additional back surgery.

Alternatives to interbody fusion surgery have been proposed includingthe use of artificial spinal disks. Such artificial spinal disks actlike cushions or “shock absorbers” between vertebrae and may contributeto the flexibility and motion of the spinal column. Thus a purpose andadvantage of such artificial spinal disks is to replace a degeneratedspinal disk, while preserving the range of motion of the spine.Replacement of a spinal disk with an artificial disk may treatunderlying back pain, while protecting patients from developing problemsat an adjacent level of the spine.

A number of different artificial disks have been proposed. For example,one such proposal includes an artificial disk primarily comprising twometal metallic plates between which is a core that allows for motion.Another proposal includes two spinal disk halves connected at a pivotpoint. Other artificial disks have been proposed in the art.

BRIEF DESCRIPTION OF THE FIGURES

Further details of embodiments of the present invention are explainedwith the help of the attached drawings in which:

FIG. 1A is a cross-sectional side-view along a sagittal plane of anartificial spinal disk positioned between adjacent vertebrae inaccordance with one embodiment of the present invention;

FIG. 1B is an enlarged side view of an anterior end of the artificialspinal disk shown in FIG. 1A;

FIG. 1C is an enlarged side view of a posterior end of the artificialspinal disk shown in FIG. 1A;

FIG. 1D is a side view of the embodiment of the invention in FIG. 1Awith internal structure shown in the dotted lines.

FIG. 1E is a side view of the embodiment of the invention in FIG. 1A.

FIG. 2A shows the artificial spinal disk of FIG. 1A during a forwardbending motion of a spine;

FIG. 2B is an enlarged side view of an anterior end of the artificialspinal disk shown in FIG. 2A;

FIG. 2C is an enlarged side view of a posterior end of the artificialspinal disk shown in FIG. 1A;

FIG. 3A is a cross-sectional side view along a sagittal plane of ananterior end of an alternative embodiment of an artificial spinal diskof the present invention showing a latch or engagement mechanism thatconnects a lower housing and an upper housing;

FIG. 3B is a cross sectional side view of an urged-together anterior endof the artificial spinal disk of the alternative embodiment shown inFIG. 3A;

FIG. 4 is a cross-sectional top plan view along a transverse plane of anartificial spinal disk in accordance with the embodiment FIG. 1A of thepresent invention;

FIG. 5A is a side view of a spacer in accordance with one embodiment ofthe present invention;

FIG. 5B is a side view of a shaft in accordance with one embodiment ofthe present invention;

FIG. 6A is a top plan view of a system in accordance with one embodimentof the present invention showing two artificial spinal disks placedside-by-side in substitution for a spinal disk;

FIG. 6B is a top plan view of another system in accordance with anotherembodiment of the present invention showing two alternative artificialdisks placed side-by-side in substitution for a spinal disk;

FIG. 6C is a top plan view of an alternative embodiment of the presentinvention showing an artificial spinal disk positioned such that a firstspacer is on a left side of a patient and a second spacer is on a rightside of a patient.

FIG. 7 is a representation of a method for replacing a degeneratedspinal disk in accordance with one embodiment of the present invention.

FIG. 8 is a plan view of an embodiment of the invention with the upperhousing removed and, which is insertable laterally into anintervertebral disk space.

FIG. 9 is a cross-section taken through line 9-9 of FIG. 8.

FIG. 10 is coss-section taken through line 9-9 of FIG. 8 with an upperhousing depicted.

FIG. 11 is an alternative embodiment of the invention with the upperhousing removed, and which is insertable laterally into anintervertebral disk space.

FIG. 12 is a cross-section taken through line 12-12 of FIG. 11 with anupper housing depicted.

FIG. 13 is a cross-section similar to FIG. 12 with the upper and lowerhousings each having two keels.

FIG. 14 is yet another an alternative embodiment of the invention withthe upper housing removed, and which is insertable laterally into anintervertebral disk space.

FIG. 15 is a cross-section taken thought line 15-15 of FIG. 14 with anupper housing depicted.

DETAILED DESCRIPTION

Systems and methods in accordance with the present invention cancomprise one or more artificial spinal disks for replacing a degeneratedspinal disk. FIGS. 1A-1C illustrate a cross-section along a sagittalplane of an artificial spinal disk 100 positioned between adjacentvertebrae in accordance with one embodiment of the present invention.The artificial spinal disk 100 comprises an upper housing 102 and alower housing 104 that combined to form a cavity 114 that partiallyenclose an anterior spacer 106 and a posterior spacer 108. The spacers106, 108 are mounted on a shaft 110 of the preferred embodiments. Thespacers 106,108 are urged apart by a spring 112 mounted concentricallyon the shaft 110. As can be seen in the Figures, the spacers 106, 108are bell shaped with an inwardly sloping cylinder side that acts as aramp relative to the upper and lower housings 102, 104. As can be seenin FIG. 5B, the shaft 110 can comprise a plurality of segments ofdifferent diameters. Shaft 110 in this embodiment is fixed to spacer 108and shaft 110 retains spacer 106 between stops. Thus spacer 106 can moverelative to shaft 110 and is urged away from spacer 108 by spring 110.

In one embodiment, a cross-section of each of the upper housing 102 andthe lower housing 104 along a sagittal plane can have inner cavities orrecesses 120, 122 that varies from an anterior end to a posterior end ofthe housing 102,104 and that have ramps 124, 126 and 128, 130respectively, such that when the upper and lower housing 102,104 areurged together, for example by a compressive or torsional force appliedto the artificial spinal disk 100, spacer 106, slides toward spacer 108.It is to be understood that in an alternative embodiment that bothspacers 106, 108 can be movably mounted on shaft 110 and thus when aload is placed on artificial spinal disk 100, both spacers 106, 108 canslide towards each other. Accordingly can be seen in FIG. 1A-1C, thecavities or recesses 120, 122 of the upper housing 102 and lower housing104 can each have a minimum depth at the anterior and posterior ends ofthe housing 102, 104 and a maximum depth approximately at the center ofthe housing 102, 104. From a position at the center of the housing 102,104 and extending outwardly in both directions, the depth of thecavities or recesses 120, 122 decrease in a linear fashion such thatramps 124, 126, and 128, 130 are formed at each of the posterior andanterior ends. In other embodiments, the ramps can vary in a non-linearfashion such that the ramps can have a concave shape or a concave shapeor a combinations of shapes.

As can be seen in FIG. 1A, the artificial spinal disk 100 also includeskeels 140 and 142 extending from the upper housing 102 and the lowerhousing 104 respectively. The keels 140 and 142 are directed in thisembodiment along a posterior/anterior line. In other embodimentsdescribed and depicted herein, the keels can be oriented laterally suchthat the keels are about perpendicular to the sagittal plane of thebody. In other words the lateral keels would be used for method whichinvolved a lateral implantation of the disk 100 relative to the spine.

In the embodiment of FIG. 1A, the keels 140, 142 each have teeth, 144,146 respectively. For embodiments that are inserted from a posterior toan anterior direction, as depicted in FIG. 1A, the teeth point in aposterior direction with a ramp facing an anterior direction. Thisconfiguration allows the keels to be more easily inserted into keelchannels cut in the vertebral bodies, and helps to lock the keels inplace. In general it is advantageous to have the teeth point in adirection that is opposite to the direction of insertion of the keelinto the bone and in this particular situation into the vertebral bodiesof the spine.

In the embodiment shown the keels include ports 148 and 150. Bone from,for example, the vertebral bodies can grow thorough the ports and aid insecuring the keels and the artificial disk 100 with respect to thevertebral bodies. In addition the keels and the surfaces of theartificial spinal disk 100 can be roughened in order to promote boneingrowth into the surfaces of the artificial spinal disk 100. By way ofexample only, such surfaces can be coated with a bone growth substancesuch as for example bone morphogenic protein, BMP or hyaluronic acid,HA, or other substance which promotes growth of bone relative to andinto the keel, keel ports, and other external surfaces of the disk 100.In addition in another embodiment these surfaces can be coated withcobalt chrome in order to provide a surface for bone-in growth relativeto the replacement disk 100.

FIGS. 2A-2C illustrate an artificial spinal disk 100 wherein an anteriorend of the upper and lower housings 102,104 are urged together. As aspacer 106 slides toward spacer 108, a gap between the upper housing 102and the lower housing 104 at the anterior end of the disk 100 lessens.For example, where a patient having an artificial spinal disk 100 bendsforward, a bending force is applied to the anterior end of theartificial spinal disk 100, causing the anterior spacer 106 to slidetoward a posterior end of the artificial spinal disk 100 by slidingalong ramps 124, 128 of the upper and lower housings 102, 104respectively. The spring 112 is compressed. As shown in FIG. 2B, one endof the shaft 110 passes through the anterior spacer 106 such that thespring 112 is compressed. It is noted that in this embodiment, thatalthough the anterior end of the upper and lower housings of theartificial spinal disk 100 are urged together, that the posterior end ofthe upper and lower housings maintains a spaced apart distance which isthe same as prior to when the force was placed on the disk 100, as forexample depicted in FIGS. 1A-1E. That is to say that the maximum heightof the disk 100 along the length of the disk 100 does not change. Thedisk 100 can be compressed at one end, with the other end either beingcompresses or maintaining the original height. This feature can beadvantageous with respect to the anatomy or the spine, as the spine, dueto ligaments and other tissues, may allow, for example, an anterior diskspace to be compressed together and may not allow an opposed posteriordisk space to be expanded. In a natural disk space of the spine, withthe anterior disk space compressed, the posterior disk space generallycan maintain the same height, or is also compressed. The embodiment ofFIGS. 3A, 3B illustrate this feature.

The anterior spacer 106 stops sliding when a component of the bendingforce urging the anterior spacer 106 to slide along the ramp is balancedby a component of force of the spring 112 on the shaft 110 urging theanterior spacer 106 apart from the posterior spacer 108, or until theupper housing 102 contacts the lower housing 104 and the gap iseliminated. When the bending force is removed from the anterior end ofthe artificial spinal disk 100, the force of the spring 112 on the shaft110 causes the anterior spacer 106 to slide toward the anterior end ofthe artificial spinal disk 110, urging the upper housing 102 and thelower housing 104 apart as the anterior spacer 106 slides on the ramps.The original gap can be restored in this manner by removing the bendingforce applied to the anterior end of the artificial spinal disk 100.Similarly, as the patient bends backward, a bending force can be appliedto the posterior end of the artificial spinal disk 100, causing theposterior spacer 108 and shaft 110 to slide toward the spacer 106 andthe anterior end of the artificial spinal disk 100.

The cross-section of the artificial spinal disk 100 shown in FIGS. 1A-2Cdepict the upper and lower housings being of the same shape. In otherembodiments, however, a cross-section of the upper housing 102 candiffer from a cross-section of the lower housing 104. For example, thelower housing 104 can be a flat plate substantially conforming to a flatsurface of one or more spacers. In still other embodiments, theposterior end of the artificial spinal disk 100 can have a differentconfiguration from the anterior end of the artificial spinal disk 100.For example, where increased stiffness is desired, the posterior end caninclude a substantially flat portion, or a portion having a steeper rampfor the spacer thereby resisting flexion from bending in the backwarddirection. One of ordinary skill in the art can appreciate the differentdevices that can allow various movements between adjacent vertebrae.

As shown in FIGS. 3A and 3B, the artificial spinal disk 100 can furthercomprise a clasp 114 or other locking mechanism connecting the upper andlower housings 102,104 together at anterior and posterior ends. Areceiving end 116 for receiving the clasp 114 is formed in the oppositehousing 102,104 so as to receive the clasp 114. The clasp 114 can beadapted to prevent the gap between the housings 102, 104 from expandingbeyond a maximum width, for example at the posterior end, when forwardbending causes flexion at the anterior end. As the spring 112 iscompressed by the sliding of the anterior spacer 106, the force appliedby the spring 112 on both the anterior spacer 106 and the posteriorspacer 108 increases. Where no restraint is applied to the posteriorend, the posterior spacer 108 can slide further toward the posteriorend, causing the gap at the posterior end to increase beyond theoriginal height. The clasp 114 can prevent expansion of the gap beyond amaximum height when a force is applied by the compressed spring 112 tothe posterior spacer 108 during forward bending. The clasp 114 canfurther prevent shifting of the upper housing 102 relative to the lowerhousing 104. In other embodiments, other mechanisms can be used. Forexample, the upper housing 102 and lower housing 104 can be tetheredtogether.

The artificial spinal disk 100 are generally anchored or fixed to thevertebrae. Fixation can be achieved, for example, as previouslydescribed by, with one or both of the upper and lower housings 102, 104including a keel 140, 142 which extend therefrom, which keels caninclude teeth 144, 146 respectively. Appropriate channels can be cut inthe upper and lower adjacent vertebrae to receive the keels 140, 142 inorder to retain the artificial spinal disk 100 relating to thevertebrae. Fixation can also be accomplished (1) by anchoring using oneor more teeth, pegs, or posts extending from the upper and/or lowerhousing 102, 104 and inserted into the vertebrae (2) by promotion ofbone-in growth by means of a porous contact surface of each housing 102,104, or (3) by fixation with screws through ports in the upper and/orlower housings 102, 104. In one embodiment, the top surface of the upperhousing 102 can include teeth which can penetrate into the top vertebra,fixing the artificial spinal disk 100 with respect to the top vertebra.Similarly, the bottom surface of the lower housing 104 can include teethwhich can penetrate into the bottom vertebra, fixing the artificialspinal disk 100 with respect to the bottom vertebra.

FIG. 4 illustrates a top down view of an artificial spinal device 100 inaccordance with one embodiment of the present invention. The upperhousing 102 and the lower housing 104 can be substantially rectangularin shape with rounded corners to ease insertion into the disk space ifdesired. A cross-section of the cavity 114 formed between the housings102, 104 along the transverse plane can be elliptical in shape such thatthe sidewalls of the cavity 120, 122 roughly conform to the shape of thespacers 106, 108, limiting shifting of the upper housing 102 relative tothe lower housing 104. In other embodiments, the cross-section of thecavities 120, 122 can have a different shape. For example, thecross-section of the cavity can be rectangular. In such a configurationthe spacers would be block shaped with upper and lower ramps. Such aconfiguration would not respond to twisting or torsional forces as wellas the embodiment shown in FIG. 4. One of ordinary skill in the art canappreciate the different configurations for the cavity.

As shown in FIGS. 4 and 5A, the anterior and posterior spacers 106, 108can be substantially ovoid-shaped or bell-shaped. Each spacer 106, 108can be radially symmetrical about an axis along the length of the cavityand can be truncated at a proximal and a distal end, for example todecrease the space occupied by the spacer 106, 108 within the cavity. Inother embodiments, the spacer 106, 108 can have a different shape, suchas, for example, a wedge shape. A bore can be formed in each spacer 106,108 for connecting the spacer 106, 108 with the shaft 110. The bore canreceive an end of the shaft 110 so that as the spacers 106, 108 areurged together, the spacers more together and relative to the shaft 110.In an alternative embodiment, the anterior spacer 106 can include atiered cylindrical bore that extends through the anterior spacer 106.This structure can provide stops to limit the motion of the spacer 106and the shaft 110 relative to each other. In still other embodiments,each spacer 106, 108 can include a collar 155 (FIG. 1A) that is receivedin a recess of the shaft 110 to limit the motion of the spacers 106, 108and the shaft 110 relative to each other. One of ordinary skill in theart can appreciate the different means and methods for connecting ashaft with a spacer.

The spacers 106, 108 and housings 102, 104 can be of various shapes andsizes. Thus for example, using imaging prior to surgery, the anatomy ofthe individual patent can be determined and the artificial spinal disk100 selected to suit the particular patient. Additionally, duringsurgery the physician can be provided with a kit having different sizedartificial spinal disks 100 to fit the anatomy of the patient.

The upper housing 102 and lower housing 104 and the spacers 106, 108 andshaft 110 can be made of stainless steel, titanium, and/or otherbio-compatible metal or metal composite. Each component can be cast,milled, or extruded, for example. Alternatively, the upper housing 102and lower housing 104 and the spacers 106, 108 and the shaft 110 can bemade of a polymer such as polyetheretherketone (PEEK), (as definedbelow) or other biologically acceptable material. A material can beselected based on desired characteristics. For example, a metal can beselected based on high relative fatigue strength. Many patients withback pain are in their lower fortie's in age. In such cases, it may bedesired that an artificial spinal disk have a fatigue life of at leastforty years, extending beyond a patients octogenarian years.

As indicated above, each spacer 106, 108 can be made of a polymer, suchas a thermoplastic, and can be formed by extrusion, injection,compression molding and/or machining techniques. Specifically, thespacer 106, 108 can be made of a polyketone such as PEEK.

One type of PEEK is PEEK 450G, which is an unfilled PEEK approved formedical implantation available from Victrex of Lancashire, GreatBritain. Other sources of this material include Gharda located inPanoli, India. PEEK 450G has appropriate physical and mechanicalproperties and is suitable for carrying the physical load exerted by theupper housing 102 and lower housing 104 while providing a smooth,slidable surface. For example in this embodiment PEEK has the followingapproximate properties: Density 1.3 g/cc Rockwell M 99 Rockwell R 126Tensile Strength 97 MPaModulus of Elasticity 3.5 GPa Flexural Modulus4.1 Gpa

The material selected may also be filled. For example, other grades ofPEEK available and contemplated include 30% glass-filled or 30%carbon-filled PEEK, provided such materials are cleared for use inimplantable devices by the FDA or other regulatory body. Glass-filledPEEK reduces the expansion rate and increases the flexural modulus ofPEEK relative to unfilled PEEK. The resulting product is known to beideal for improved strength, stiffness, or stability. Carbon-filled PEEKis known to enhance the compressive strength and stiffness of PEEK andlower its expansion rate. Carbon-filled PEEK offers wear resistance andload carrying capability.

As will be appreciated, other suitable bio-compatible thermoplastic orthermoplastic polycondensate materials that resist fatigue, have goodmemory, are flexible and/or deflectable, have very low moistureabsorption and have good wear and/or abrasion resistance, can be usedwithout departing from the scope of the invention. Other materials thatcan be used include polyetherketoneketone (PEKK), polyetherketone (PEK),polyetherketoneetherketoneketone (PEKEKK), andpolyetheretherketoneketone (PEEKK), and generally apolyaryletheretherketone. Further, other polyketones can be used, aswell as other thermoplastics.

Reference to appropriate polymers that can be used in the spacer can bemade to the following documents, all of which are incorporated herein byreference: PCT Publication WO 02/02158 A1, dated Jan. 10, 2002 andentitled Bio-Compatible Polymeric Materials; PCT Publication WO 02/00275A1, dated Jan. 3, 2002 and entitled Bio-Compatible Polymeric Materials;and PCT Publication WO 02/00270 A1, dated Jan. 3, 2002 and entitledBio-Compatible Polymeric Materials. Other materials such as Bionateg,polycarbonate urethane, available from the Polymer Technology Group,Berkeley, Calif., may also be appropriate because of the good oxidativestability, biocompatibility, mechanical strength and abrasionresistance.

Other thermoplastic materials and other high molecular weight polymerscan be used. One of ordinary skill in the art can appreciate the manydifferent materials with which a spacer 106, 108 having desiredcharacteristics can be made.

FIG. 6A illustrates a top down view of a system comprising twoartificial spinal disks 100 in accordance with one embodiment of thepresent invention. A device or system is typically designed to occupyapproximately an entire cross-sectional area of the vertebra so that aspinal load can be distributed over a maximum surface area. A singleartificial spinal disk sized to occupy the entire cross-sectional areamay complicate surgical insertion that requires implantation of theartificial spinal disk through an open anterior approach. To minimizethe incision size, a plurality of artificial spinal disks can form asystem in accordance with one embodiment of the present invention forreplacing a degenerative spinal disk. By implanting each artificialspinal disk 100 separately, a smaller incision is required, therebyallowing for a posterior approach. As shown in FIG. 6A, the system cancomprise two artificial spinal disks 100. However, in other systemsthree or more artificial spinal disks can be used, or even a singleartificial spinal disk. The size of each artificial spinal disk and thenumber of artificial spinal disks connected can depend on the locationof the adjacent vertebrae (for example the defective spinal disk may bea lumbar disk or thoracic disk), the preferences of a surgeon or thepreferences of a patient, for example.

First and second artificial spinal disks 100 can be connected togetherat one or more locations, preferably along opposing surfaces, preventingshifting of one artificial spinal disk 100 relative to the other. Theartificial spinal disks 100 can be connected using one or more snaps,pins, screws, hinges or other fastening device 111. One of ordinaryskill in the art can appreciate the methods for connecting multipleartificial spinal disks 100 after each disk 100 is separately implantedbetween adjacent vertebrae.

By way of example, an incision can be made posteriorly from the left orright of the spinous processes. The disk space can be cleaned and tissueremoved as required. Then disk 100 can be inserted through the incision.Thereafter, the second disk can be inserted into the disk space throughthe disk space through the incision. Once the second disk 100 ispositioned the two disks can be secured together by for exampleinserting a pin or screw between aligned eyelets extending form thedisks 100 as seen in FIG. 6A.

As can be seen in FIGS. 6B, 6C in other embodiments, an artificialspinal disk 600 can comprise a first spacer 606 and a second spacer 608,each spacer being positioned at an opposite end of a shaft 610, whichshaft is substantially parallel to a sagittal plane. The shaft 610allows for urging the spacers 606, 608 toward each other. The artificialspinal disk 600 permits flexion from side to side. The artificial spinaldisk 600 can comprise an upper housing 102 and a lower housing 104 thattogether form a “kidney bean” shaped cavity 612. The kidney shapedcavity 612 can accommodate side to side bending with simultaneoustwisting or tortional motion of the spine. The separate disks 600 can beimplanted and joined together or described above with respect to FIG.6A.

FIG. 7 is a block diagram showing steps for performing a method forinserting a disk 100 into a patient in order to replace a degeneratedspinal disk or otherwise defective spinal disk in accordance with thepresent invention and using a posterior, anterior or lateral approach.As shown in first block 700, an artificial spinal disk is selectedaccording to the size of the spinal disk to be replaced and the degreeand character of the freedom of movement desired. In one embodiment, afirst and second artificial spinal disk 100 as shown in FIGS. 1A-1E canbe selected. In an alternative embodiment, a single artificial spinaldisk 600 as shown in FIG. 14 can be selected. An incision is made in thepatient proximate to the defective spinal disk (step 702), and thespinal disk and surrounding tissues are exposed. The adjacent vertebraeare braced (if required), so that the defective spinal disk can beremoved (if required), allowing for replacement by the artificial spinaldisks 100 (step 704). An artificial spinal disk 100 can be insertedthrough the incision and positioned between the adjacent vertebrae (step706). For this procedure, the nerve and other structures of the spinalcolumn can be retracted out of its way. Minor adjustments in positioningcan then be made (step 710) followed by removing the braces (if used)(step 712). The incision is closed (step 714).

Also it is to be understood that as described below, an artificialspinal disk can be inserted laterally into a disk space between twoadjacent vertebral bodies. In this method the spine is approachedlaterally and disk tissue is removed as is appropriate. Then the disk100 is inserted along a lateral direction.

Other methods of insertion include having the disk 100 disassembledprior to insertion. For this method, an upper or a lower housing 102,104 can first be inserted and either loosely positioned or fixed to avertebra, followed by a first spacer 106, a shaft 110, and a secondspacer 108. The housing 102, 104 can then be joined or snapped togetherusing the mechanism shown in FIGS. 3A, 3B. The procedure can be repeatedfor multiple artificial spinal disks.

FIGS. 8-15 depict artificial spinal disks that are preferably insertedusing a lateral approach to the spine along a direction that issubstantially perpendicular to a sagittal plane of the spine.

In these embodiments, elements that are similar to the elements of priorembodiments are similarly numbered. In FIGS. 8-10 an artificial spinaldisk 800 includes upper and lower housings 802 and 804 which togetherdefine a cavity 814 that partially enclose lateral spacers 806 and 808.The spacers 806 and 808 are mounded on a shaft 810 with a spring 812moved over the shaft so as to urge spacers 806 and 808 apart. Thespacers in this embodiment are larger, broader and flatter than thespacers in prior embodiments in order to carry and spread out the loadfrom the spinal column.

As can be seen in FIGS. 9 and 10, the spacers 802, 804 are somewhatelliptical or football shaped in cross-section. In the plan view of FIG.8, the spacers 802, 804 are depicted as somewhat wing-tip shaped. Thespacers 806, 808 are received in cavities or recesses 820, 822 providedin the upper and lower housings 802, 804 respectively. These recessesare similar to recesses 120, 122 although somewhat flatter. Theserecesses 820, 822 have the same cross-section as do recesses 120, 122 asseen in FIG. 1A in that each includes a ramp at either end of the recesswith a central portion having a greater depth than the ramped portionsof the recesses. The spacers 806, 808 are similarly mounted on the shaft810 as are spacers 106, 108 mounted on shaft 110.

The upper and lower housings 802, 804 further include keels 840 and 842which can be similar in design as keels 140 and 142. In this embodiment,however, the keels 840, 842 are provided along a lateral orientationwith respect to the spine. In order words, the keels are provided ondisk 800 so that after disk 800 is implanted, the keels aresubstantially perpendicular to the sagittal plane of the spine. Thekeels 802, 804 are preferably provided parallel to and over the shaft810 in order to balance the load of the spine on the disk 800. Such anarrangement provides stability to the disk 800 with respect to bendingof the spine from flexion to extension in the sagittal plane.

The present embodiment is preferably implanted laterally orsubstantially perpendicular to the sagittal plane of the spine.Accordingly the method of implantation is similar to that described inFIG. 7 except that the approach to the spine is laterally instead of aposterior approach.

FIGS. 11-13 depict another embodiment of the invention that ispreferably implanted laterally or substantially perpendicularly to thesagittal plane of the spine. In this embodiment elements similar toelements of prior embodiments are similarly numbered. In thisembodiment, however, each implant includes two pairs of spacers 1106,1108 which are mounted on substantially parallel shafts 1110 and urgedapart by springs 1112. It is to be understood that the shafts 1110 canbe other than parallel and be within the spirit and scope of theinvention. For example the shafts can be placed in somewhat of a “v”shape with the base of the “v” pointed to the posterior of the spine andthe open end of the “v” pointed to the anterior of the spine. Thespacers 1106, 1108 are preferably similar in shape to the bell shapedspacers in FIG. 1. The recess 1122 is similar in shape, having the rampsat the ends as the recesses 122 in the first disk embodiment 100. Thedisk 1100 operates in the same manner as the disk 100 or to be morespecific, similar to two disks 100, placed side-by-side. As the disk1100 can be implanted laterally, there is no need to have the diskdivided into two portions as is the case with the disk of FIG. 6A whichis implanted with a posterior approach. Further it is to be understoodthat the disk 1100 can also be inserted using an anterior approach.

As can be seen in FIGS. 12, 13 the lateral implantation approach ispreferred due to the laterally oriented keels 1140, 1142. These keelsare similarly oriented as are the keels depicted in FIGS. 9, 10. In FIG.13 both the upper and the lower housings include a pair of keels 1140,1142 respectively, with the keels preferably located over the spacers1106, 1108. The keels can have the same ports and bone ingrowthenhancements as the other keels described above.

With respect to FIGS. 14, 15 the artificial spinal disk 1400 includeselements that are similar to those described above and these elementsare similarly numbered. This embodiment is also preferably implantedusing a lateral approach although an anterior approach can also be used.The embodiment of these figures has spacers 1406, 1408 which are similarin design to the spacers of the embodiment of FIG. 8-11 with theexception that the shaft 1410 and spring 1412 are oriented along ananterior/posterior direction and not laterally as shown in FIG. 8. Thespacers 1406, 1408 are received in recess 1422. This embodiment alsoincludes laterally disposed keels 1440, 1442 with all of the aboveadvantages attendant with laterally disposed keels.

It is to be noted that in a number of these Figures the implants areillustrated against a kidney-shaped background that is representative ofthe plan view shape of the disk space between vertebral bodies.

The foregoing description of preferred embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many modifications andvariations will be apparent to one of ordinary skill in the relevantarts. The embodiments were chosen and described in order to best explainthe principles of the invention and its practical application, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with various modifications that are suited tothe particular use contemplated. Other features, aspects, and objects ofthe invention can be obtained from a review of the specification, thefigures, and the claims. It is intended that the scope of the inventionbe defined by the claims and their equivalence.

1. An artificial replacement disk that is positionable between vertebraecomprising: an upper housing including an upper cavity; a lower housingincluding a lower cavity; a first spacer and a second spacer, said firstand second spacers mounted on a shaft with a resisting member locatedbetween the first and the second spacers, which resisting member canurge said first and second spacers apart; and said first and secondspacers partially located in said upper cavity and partially located insaid lower cavity.
 2. The disk of claim 1 wherein at least one of saidupper cavity and said lower cavity includes a ramp and at least one ofsaid first spacer and said second spacer can slide relative to saidramp.
 3. The disk of claim 1 wherein at least one of said upper cavityand said lower cavity includes a ramp and at least one of said firstspacer and said second spacer can slide relative to said ramp in orderto allow said first housing to move relative to said second housing. 4.The disk of claim 1 wherein at least one of said upper cavity and saidlower cavity includes a ramp and at least said first spacer and saidsecond spacer includes a ramp with can mate with the ramp of the atleast one of said upper cavity and said lower cavity.
 5. The disk ofclaim 1 wherein when the upper housing and the lower housing are urgedtogether, said first spacer and said second spacer move relative to eachother.
 6. The disk of claim 1 wherein when the upper housing and thelower housing are urged together, one of the first spacer and the secondspacer moves toward the other of the first spacer and the second spacer.7. The disk of claim 1 wherein when the upper housing and the lowerhousing are urged together, the first spacer and the second spacer movestoward each other.
 8. The disk of claim 1 including a retainer thatmaintains no more that a maximum distance between the upper housing andthe lower housing.
 9. The disk of claim 1 wherein at least one of theupper cavity and the lower cavity is concave in shape.
 10. The disk ofclaim 1 wherein at least one of the upper cavity and the lower cavityhas a first sloping end, a central cylindrical portion, and a secondsloping end.
 11. The disk of claim 1 wherein at least one of the uppercavity and the lower cavity is kidney shaped.
 12. The disk of claim 1wherein at least one of the upper cavity and the lower cavity issubstantially elliptically shaped.
 13. The disk of claim 1 wherein atleast one of the first spacer and the second spacer includes a ramp. 14.The disk of claim 1 wherein at least one of the first spacer and thesecond spacer is oval-shaped.
 15. The disk of claim 1 wherein at leastone of the first spacer and the second spacer is bell-shaped.
 16. Anartificial replacement disk that is positionable between vertebraecomprising: a first housing including a first cavity; a second housingincluding a second cavity; a first spacer and a second spacer, saidfirst and second spacers mounted on a shaft with a resisting memberlocated between the first and the second spacers, which resisting membercan urge said first and second spacers apart; and said first and secondspacers partially located in said first cavity and partially located insaid second cavity; and when the first housing is urged toward thesecond housing the first and the second spacers move relative to eachother and against the resisting member.
 17. The disk of claim 16 whereinsaid first and said second housings have first and second elongatedsides respectively, and wherein at least one of the first and secondspacers can move along a direction of the first and second elongatedsides, such that when the first and second housing are urged together atan angle that is non-parallel to at least one of the first and secondelongated sides, the at least one of the first and second spacers movealong the direction of the first and the second elongated sides.
 18. Thedisk of claim 16 wherein at least one of the first cavity and the secondcavity has a first sloping end, a central cylindrical portion, and asecond sloping end.
 19. An artificial replacement disk that ispositionable between vertebrae comprising: an first housing and a secondhousing; and means located between the first housing and the secondhousing for moving at an angle with respect to a direction that thefirst housing and the second housing can be urged together in order toabsorb energy when the first housing and the second housing are urgedtogether.
 20. An artificial replacement disk comprising: a housing thatcan move in a first direction in order to move a spacer along thehousing in a second direction in order to change the over all dimensionsof the housing.
 21. An artificial replacement disk that is positionablebetween vertebrae comprising: a first housing including a cavity; asecond housing; a first spacer and a second spacer, said first andsecond spacers mounted on a shaft with a resisting member locatedbetween the first and the second spacers, which resisting member canurge said first and second spacers apart; said first and second spacersat least partially located in said cavity; wherein the cavity has asloping portion, and a cylindrical portion; and when the first housingis urged toward the second housing the first and the second spacers moverelative to each other and against the resisting member with one of thefirst and second spacers moving along the sloping portion of the cavityand toward the cylindrical portion.
 22. An artificial spinal diskadapted to be positioned between adjacent vertebrae of a spine,comprising: an upper plate; a lower plate positioned opposite the upperplate such that a gap having a maximum width exists between the lowerplate and the upper plate; a device that can urge the upper and lowerplates apart; and wherein when the upper plate and the lower plate areurged together, the gap between a portion of each of the upper plate andthe lower plate narrows, such that the gap between a remaining portionof each of the upper plate and the lower plate is no wider than themaximum width.
 23. The artificial spinal disk of claim 22, furthercomprising: at least one spacer positioned between the upper plate andthe lower plate; wherein when the upper plate and lower plate are urgedtogether, the at least one spacer slides away relative to the housing.24. The artificial spinal disk of claim 22, further comprising: a firstspacer positioned between an first portion of the upper plate and anfirst portion of the lower plate; a second spacer positioned between asecond portion of the upper plate and a second portion of the lowerplate; and wherein when the upper plate and lower plate are engagedtogether, one or both of the first spacer and the second spacer slidetoward each other.
 25. The artificial spinal disk of claim 24, furthercomprising: a shaft positioned such that at least a portion of the shaftis between the first spacer and the second spacer; wherein a load isapplied along the shaft, the load urging the first spacer and the secondspacer apart.
 26. The artificial spinal disk of claim 25, furthercomprising: a spring associated with the shaft for applying the load.27. The artificial spinal disk of claim 24, wherein a cavity of at leastone of the upper plate and the lower plate includes a ramp.
 28. Theartificial spinal disk of claim 24, wherein a cavity at least one of theupper plate and the lower plate is kidney shaped.
 29. The artificialspinal disk of claim 27, wherein the first spacer has a substantiallyovoid-shaped cross-section such that the first spacer substantiallyconform to the ramp of at least one of the upper plate and the lowerplate.
 30. The artificial spinal disk of claim 27, wherein the firstspacer has a substantially bell-shaped cross-section such that the firstspacer substantially conforms to the ramp of at least one of the upperplate and the lower plate.
 31. The artificial spinal disk of claim 28,wherein the first spacer has a substantially oval-shaped cross-sectionsuch that the first spacer substantially conforms to at least one of theupper plate and the lower plate.
 32. The artificial spinal disk of claim28, wherein the first spacer has a substantially bell shapedcross-section such that the first spacer substantially conform to atleast on of the upper plate and the lower plate.
 33. The artificialspinal disk of claim 22, further comprising: a latch mechanism connectedwith at least one of the upper plate and the lower plate; a receivingmechanism connected with at least one of the upper plate and the lowerplate that can receive the latch mechanism; and wherein the latchmechanism prevents at least a portion of the gap expanding beyond amaximum width.
 34. The artificial spinal disk of claim 22, wherein theupper plate and lower plate each comprise one of titanium, stainlesssteel, or PEEK.
 35. The artificial spinal disk of claim 24, wherein thefirst spacer and the second spacer each comprise one of titanium,stainless steel, or PEEK.
 36. The artificial spinal disk of claim 22,further comprising: a plurality of ridges on at least one of the upperplate and lower plate adapted to grip an associated vertebra.
 37. Anartificial spinal disk adapted to be positioned between adjacentvertebrae of a spine, comprising: a first portion, including: a firstupper plate; a first lower plate positioned opposite the first upperplate such that a gap having a maximum width exists between the firstlower plate and the first upper plate; a first device that can urge thefirst upper and first lower plates apart; and wherein when the firstupper plate and the first lower plate are urged together, the gapbetween a portion of each of the first upper plate and the first lowerplate narrows, such that the gap between a remaining portion of each ofthe first upper plate and the first lower plate is no wider than themaximum width; a second portion, including: a second upper plate; asecond lower plate positioned opposite the second upper plate such thata gap having a maximum width exists between the second lower plate andthe second upper plate; a second device that can urge the second upperand second lower plates apart; wherein when the second upper plate andthe second lower plate are urged together, the gap between a portion ofeach of the second upper plate and the second lower plate narrows, suchthat the gap between a remaining portion of each of the second upperplate and the second lower plate is no wider than the maximum width; adevice that can join the first portion with the second portion.
 38. Aartificial spinal disk for substituting at least a portion of a spinaldisk between adjacent vertebrae, comprising: an upper housing adapted tobe positioned adjacent to a first vertebra; a lower housing positionedopposite the upper housing, the lower housing adapted to be positionedadjacent to a second vertebra; an first spacer positioned between theupper housing and the lower housing such that an first gap can existbetween an first end of the upper housing and an first end of the lowerhousing; a second spacer positioned between the upper housing and thelower housing such that a second gap can exist between a second end ofthe upper housing and a second end of the lower housing; a shaft; thefirst spacer and the second spacer mounted on the shaft; a device thatcan urge the first and second spacer apart; and wherein when the upperhousing and the lower housing are urged together, the space between thefirst spacer and the second spacer can be reduced.
 39. The artificialspinal disk of claim 38, wherein the shaft includes a spring forapplying the load.
 40. The artificial spinal disk of claim 38, wherein acavity of at least one of the upper housing and the lower housing has aramp.
 41. The artificial spinal disk of claim 38, wherein a cavity of atleast one of the upper housing and the lower housing is kidney-shaped.42. The artificial spinal disk of claim 40, wherein the first spacer hasa substantially oval-shaped cross-section such that the first spacersubstantially conforms to the ramp at least one of the upper housing andthe lower housing.
 43. The artificial spinal disk of claim 40, whereinthe first spacer has a substantially bell-shaped cross-section such thatthe first spacer substantially conforms to the ramp of at least one ofthe upper housing and the lower housing.
 44. The artificial spinal diskof claim 38, wherein when the upper housing and the lower housing areurged together, the first spacer slides along the upper housing and thelower housing and in a cavity to reduce the space between the firstspacer and the second spacer.
 45. The artificial spinal disk of claim38, further comprising: a latch mechanism on at least one of the upperhousing and the lower housing; a receiving mechanism that can receivethe latch mechanism on at least the other of the upper housing and thelower housing; and wherein the latch mechanism prevents the upper andlower housing from expanding beyond a desired distance.
 46. Theartificial spinal disk of claim 38, wherein the upper housing and lowerhousing each comprise one of titanium, stainless steel, or PEEK.
 47. Theartificial spinal disk of claim 38, wherein the first spacer and thesecond spacer each comprise one of titanium, stainless steel, or PEEK.48. The artificial spinal disk of claim 38, further comprising: a ridgeon at least one of the upper housing and lower housing for gripping anassociated vertebra.
 49. The disk of claim 22 wherein: the first andsecond spacers have shapes of revolution.
 50. The disk of claim 22wherein: said first and second spacers have first and second spacerramps respectively.
 51. The disk of claim 22 wherein: said first andsecond spacers each have housing contact surfaces that are wider thanthe spacers are tall.
 52. The disk of claim 22 wherein: said first andsecond spacers are conically-chaped with rounded edges.
 53. Anartificial spinal disk that is adapted to be placed between adjacentvertebral bodies of a spine, comprising: an upper elongated housing; alower elongated housing; a first spacer and a second spacer positionedrelative to an elongated shaft between the first and second housingswith the elongated shaft being about parallel to the upper and lowerelongated housings; a spring mechanism positioned along said shaft inorder to urge said first and second spacers apart; and wherein when theupper and lower housings are urged together at least one of the firstand second spacers can move relative to the other against the springmechanism
 54. The disk of claim 53 wherein: the first and second spacershave shapes of revolution.
 55. The disk of claim 53 wherein: said firstand second spacers have first and second spacer ramps respectively. 56.The disk of claim 1 wherein at least one of the housings includes a keeladapted to be positioned in a vertebral body of a vertebra.
 57. The diskof claim 1 wherein at least one of the housings includes a keel that ispositioned on said at least one housing so that with the disk implantedin a spine the keel is oriented laterally with respect to the spine. 58.The disk of claim 1 wherein at least one of the housings includes a keelthat is positioned on said at least one housing so that with the diskimplanted in a spine the keel is substantially perpendicular to asagittal plane of the spine.
 59. The disk of claim 1 wherein said upperand lower housings with no force on the disk are spaced apart a maximumamount and force on any portion of the disk does not space the housingsapart beyond said maximum amount.
 60. The disk of claim 1 wherein withthe disk implanted in a spine the shaft is adapted to be oriented alonga lateral line with respect to the spine.
 61. The disk of claim 1wherein with the disk implanted in a spine the shaft is adapted to beoriented along an anterior/posterior line.
 62. The disk of claim 16including at least one of said first and second housings including akeel that is adapted to be positioned in a vertebral body of the spine.63. The disk of claim 16 wherein at least one of the housings includes akeel that is positioned on said at least one housing so that with thedisk implanted in a spine the keel is oriented laterally with respect tothe spine.
 64. The disk of claim 16 wherein at least one of the housingsincludes a keel that is positioned on said at least one housing so thatwith the disk implanted in a spine the keel is substantiallyperpendicular to a sagittal plane of the spine.
 65. The disk of claim 16wherein said first and second housings with no force on the disk arespaced apart a maximum amount and force on any portion of the disk doesnot space the housings apart beyond said maximum amount.
 66. The disk ofclaim 16 wherein with the disk implanted in a spine the shaft is adaptedto be oriented along a lateral line with respect to the spine.
 67. Thedisk of claim 16 wherein with the disk implanted in a spine the shaft isadapted to be oriented along an anterior/posterior line.
 68. The disk ofclaim 1 including BMP provided thereon.
 69. The disk of claim 16including BMP provided thereon
 70. An artificial replacement disk thatis positionable between vertebrae comprising: a first housing includinga first cavity and a second cavity; a second housing including a thirdcavity and a fourth cavity; wherein the first cavity and the thirdcavities are aligned with each other and are provide along ananterior/posterior line relative to a spine when the disk is implantedin a spine; wherein the second cavity and the fourth cavities arealigned with each other and are provide along an anterior/posterior linerelative to a spine when the disk is implanted in a spine; a firstspacer and a second spacer, said first and second spacers mounted on afirst shaft with a first resisting member located between the first andthe second spacers, which first resisting member can urge said first andsecond spacers apart; and said first and second spacers partiallylocated in said first cavity and partially located in said secondcavity; a third spacer and a fourth spacer, said third and fourthspacers mounted on a second shaft with a second resisting member locatedbetween the first and the second spacers, which second resisting membercan urge said third and fourth spacers apart; and said third and fourthspacers partially located in said third cavity and partially located insaid fourth cavity; and when the first housing is urged toward thesecond housing at least one of the first and the second spacers moverelative to each other and against the first resisting member and thethird and fourth spaces move relative to each other and against thesecond resisting member.
 71. The disk of claim 70 including at least oneof the first and second housings includes a keel extending therefrom,which keel is laterally oriented with the disk implanted in a spine. 72.The disk of claim 70 including at least one of the first and secondhousings including a keel extending therefrom, which keel is orientedabout perpendicular to a sagittal plane of a spine with the diskimplanted in a spine.
 73. The disk of claim 1 wherein the first andsecond spacers are oval in cross-section.
 74. The disk of claim 1wherein the first and second spacers are elliptical in cross-section.